1. Field of the Invention
The present invention relates to a vibration-damping device adapted to be attached to a vibrative member so as to constitute a secondary vibration system for the vibrative member as a primary vibration system, to thereby damp vibrations excited in the vibrative member.
2. Description of the Related Art
A dynamic damper is known as one type of vibration-damping device for damping vibrations excited in a vibrative member that is likely to be vibrated, such as a body of an automotive vehicle. Such a conventional dynamic damper includes a mass member and a spring member for elastically supporting the mass member with respect to the vibrative member, so that the dynamic damper constitutes a secondary vibration system for the vibrative member as a primary fluid system. In the conventional dynamic damper, a natural frequency of the secondary vibration system may be tuned to a frequency band of vibrations excited in the vibrative member, namely, vibrations to be damped, whereby the dynamic damper is capable of exhibiting a desired vibration-damping effect with respect to the vibrative member.
However, the vibration-damping effect of the conventional dynamic damper is limited to a very narrowed frequency range to which the secondary vibration system is tuned. In particular, the presence of the dynamic damper may possibly excite vibrations or a peak in amplitude of the vibrations at other two frequency ranges higher and lower than the frequency range to which the secondary vibration system is tuned, resulting in undesirable deterioration of a vibrating state of the vibrative member.
To cope with this problem, it is considered to form the spring member in the second vibration system of a rubber elastic body having a high damping characteristic, in an attempt to assure a high damping capability with respect to vibrations over a wide frequency range, and to moderate or improve a vibrating state of the vibrative member at the higher and lower frequency range with respect to the frequency range to which the secondary vibration system is tuned.
However, the dynamic damper having the spring member formed of the rubber elastic body is likely to exhibit its damping characteristic influenced by the ambient temperature, since a damping capability of the rubber elastic body has a high temperature dependency. When the dynamic damper is installed in a portion where the ambient temperature widely varies, the damping characteristic of the dynamic damper inevitably varies, leading to possible deterioration of the damping effect of the dynamic damper with respect to intended frequency range. For instance, when the dynamic damper installed on a power unit or an exhaust pipe of an automotive vehicle, the dynamic damper exposed to a relatively wide variation of the ambient temperature ranging from minus several tens to plus one hundred degrees Celsius or more. In this case, the dynamic damper inevitably experiences undesirable variation of its damping characteristic, hence suffering from a problem of difficulty in exhibiting an intended damping effect with high stability.